1. Field of the Invention
The present invention relates to an amplifier having output protection, in particular to an operational amplifier for audio application.
2. Discussion of the Related Art
As known, in audio systems, it is necessary to avoid destruction of the power output transistors of operational amplifiers. In particular, the operational amplifiers are to be protected when connected to loads having excessively low resistance, in particular in order to avoid the occurrence of short-circuits on the output stage of the operational amplifier, the schematic circuit whereof is shown in FIG. 1.
To this end, prior art protection circuits senses the output current IOUT flowing to the load RL. When the sensed current IOUT exceeds a reference value, a feedback circuit decreases the gain of the operational amplifier OPAMP. In practice, the prior art protection circuits provide a characteristic of the output current IOUT versus the load RL as shown in FIG. 2, wherein the output current IOUT has a constant value IMAX when the load is lower than a minimum value RLmin, and is inversely proportional to the output load, when the load is higher than the minimum value RLmin.
With the known solutions, there exists the problem that the circuit delivers a high output current when the protection circuit is active, thereby causing high power dissipation or even the destruction of the amplifier due to the heat.